As the population of the world increases, efficient mechanisms for obtaining sources of energy, including natural gas, oil and geothermal reserves are continuously being investigated. One exemplary technique for obtaining access to natural gas, oil and geothermal reserves is known as hydraulic fracturing. Hydraulic fracturing is the process of initiating and subsequently propagating a fracture in a geologic formation through utilization of fracturing fluid. To create the fracture in the geologic formation, a drill is employed to create a well bore that reaches depths of several thousand feet (until a desired geologic formation is reached). A well casing is placed in the well bore. The well casing is typically composed of steel. The well casing is cemented in place to stabilize the well casing with respect to the Earth.
Hydraulic fracturing is commonly employed to enhance the fluid flow permeability of shale geologic formations for petroleum (oil and/or natural gas) and geothermal energy production. Subsequent to the well casing being cemented in place, a fracturing fluid pumped down the well bore and through perforations in the well casing at a pressure that is in excess of the fracture gradient of the geologic formation. Such pressure causes the geologic formation to fracture. Pumping of the fracturing fluid down the well bore is continued to extend the fracture further into the formation. As the fracture extends, a proppant is added to the fracture fluid and pumped down the well bore and into the fracture, thereby propping the fracture open when pumping of the fracture fluid ceases. This causes the geologic formation to become permeable via the fracture, thereby allowing natural gas or oil to be extracted from the geologic formation. Hydraulic fractures can be induced using vertical, horizontal and/or slanted wells. This process is commonly referred to as hydraulic fracturing.
Because a typical fracture occurs thousands of feet beneath the surface of the Earth and because a fracture can extend from the well bore in a variety of directions and orientations, it is difficult to determine the location of a fracture within the geologic formation. Modeling techniques have been developed in which, prior to a hydraulic fracturing operation, electromagnetic fields at the surface of the Earth resulting from an application of an electric current to various hypothetical fractures through the well bore are calculated. Following the hydraulic fracturing operation, an electromagnetic field measured at the surface of the Earth is used to select from the various hypothetical fractures. Although these modeling techniques have been successful in helping to locate induced fractures, they are limited by the number and accuracy of the hypothetical fractures used to compute the predicted fields.
In contrast to these forward modeling approaches, an inverse modeling solution in which measured fields are used to infer the location and orientation of the fracture, rather than simply selecting from a group of hypothetical fractures, has long been desired. However, in order to infer fracture location, orientation, geometry, etc., from measured EM field data using conventional techniques, EM field data must be computed and compared with the measured field data many times. Because the computation time for computing a model can be long, it has been economically and practically infeasible to wait for this type of inverse model computation after a hydraulic fracturing operation and before the extraction of the natural gas, oil or geothermal resources. No economically and computationally feasible inverse modeling solution has therefore been forthcoming.
It would therefore be desirable to provide improved systems and methods for evaluating well hydraulic fracturing and completion techniques useful in extracting natural gas, oil and geothermal reserves from a geologic formation.